Impulse turbine, particularly of the reversible type

ABSTRACT

An impulse turbine, particularly of the reversible type, comprises at least a runner fast on a shaft in order to be rotatable about an axis of rotation. Each runner is provided with at least a hollow working member adapted to receive a fluid fed according to a direction substantially transverse with respect to said axis of rotation, from an inlet portion to a discharge portion of the hollow working member, so that thrust forces are generated whose resultant tends to drive the runner into rotation as a result of the passage of the fluid in the hollow working member. The distance between the straight line of action of the resultant of the thrust forces on each hollow working member and the axis of rotation of the runner is smaller than the distance between the inlet portion of each hollow working member and the axis of rotation of the runner.

BACKGROUND OF THE INVENTION

The present invention refers to fluid rotary machines, for example ofhydraulic, steam or gas type, which can be used in particular asturbines and as pumps.

More specifically the invention refers to an impulse turbine, that is inwhich the pressure potential energy of the fluid is transformed entirelyinto kinetic energy solely in the distributor and not in the runner.

More in particular, the invention relates to an impulse turbine havingthe features recited in the preamble of annexed claim 1.

SUMMARY OF THE INVENTION

A typical impulse hydraulic turbine is the Pelton wheel turbine.Machines of such a kind turn out to be advantageous with respect toother turbines because they are simple constructively, reliable inoperation, with a high efficiency and easy to maintain. However, usuallythey are used with great heights of fall of the water, being notrecommended or not very efficient with small and medium heights of fall.The small or medium heights, which are the most common in nature andtherefore those which are more promising in view of the exploitation byhydroelectric power plants, can be used in practice by using reactionhydraulic turbines, such as Francis or Kaplan turbines, requiring muchmore expensive plants with a more complex maintenance, at least in orderto avoid the risk that cavitation phenomena may be triggered on theblades of the respective runners.

The main problem affecting Pelton wheel turbines consists in the factthat their constructive geometry is not very flexible and is poorlyadapted to allow the change of the speed of rotation of their runnersdepending on the necessity, when the speed of the fluid fed to eachrunner is fixed.

The geometry and the operation of a runner of a Pelton wheel turbine arerepresented in principle in FIG. 1 of the drawings.

In this figure, a blade 12 of the runner 10 is hit by a fluid spoutdirected tangentially with respect to the runner 10 with a true speed V,whose straight line of action is at a distance R from the axis ofrotation of the runner 10, that is from a plane which passes along theaxis of rotation of the runner 10 and is parallel to the speed V (whichis schematically indicated in this figure by a dotted line). After thefluid has discharged a part of its energy on the blade 12, it comes outfrom it with a speed u smaller than V. As a result of the thrust appliedby the fluid, the blade 12 is subject to the action of forces whoseresultant F, at least as a first approximation and overlooking thefriction forces, can be considered acting at a point close to the centreof the blade 12, which substantially corresponds with the geometriccentre of the same blade. The resultant F can be represented by a vectorwhose straight line of action is at a distance corresponding to theradius r from the centre of the runner 10, in this case beingapproximately r=R. The resultant F acts on the relative blade 12 so asto originate a moment with respect to the centre of the runner 10 and tocause it to rotate with an angular velocity ω having, in this figure, acounter-clockwise direction.

In the solution schematically illustrated in FIG. 1, when the workingconditions are defined, in practice when the speed V of the fluid fed tothe runner 10 is defined, to a change of the radius r corresponds achange of the angular velocity ω of the runner. More concretely, areduction of the radius r implies an increase of the angular velocity ω.

The possibility to change the angular velocity ω of the runner isparticularly interesting in the case of the hydraulic turbines, since itallows to adjust the speed of a machine to the demand of the currentgenerator associated with the shaft of its runner, in other words itallows to adjust the speed of the machine to the demand of the electricnetwork to which it is associated. In the practical case of a turbine onwhose shaft a bipolar alternator is fast for the direct production of 50Hz alternated electric power, the speed of rotation of the runner mustbe 3000 r.p.m. Should it be possible to change the aforesaid radius r atwill, an angular velocity ω corresponding to 3000 r.p.m. could beobtained in practice for any absolute speed V of the fluid fed to therunner.

In a turbine of the type considered above and schematized in FIG. 1, itis not possible to change the radius r at will owing to geometric andconstructive reasons. In particular, it is not possible to reduce theradius r at will, since the reduction of the diameter of the runnerbeyond a determined limit would imply the drastic reduction of thenumber of the blades or the fact that adjacent blades may cover eachother and, in both these cases, it would cause the reduction of thecapacity of the machine to produce energy.

In order to overcome these drawbacks, the subject of the invention is animpulse turbine having the features stated in claim 1.

Thanks to this idea of solution, in an impulse turbine according to theinvention the working members of each runner can be made so that thedistance of the point at which the resultant of the forces acting oneach of them with respect to the centre of the relevant runner acts, canbe changed at will in order that the angular velocity of the runner canbe changed at will for a given speed of the fluid fed to it. In thisway, the performances of the machine can be adapted to the operationaldemands coming from the outside environment. The possibility to changeat will the angular velocity of each runner for a prefixed speed of thefluid fed to the machine, allows in practice to made the machine almostindependent from the height of fall of the fluid, when the machine hasbeen used as an hydraulic turbine. As a consequence, the height of fallof the fluid can also be small or very small, so that a turbineaccording to the invention turns out to be very versatile. Inparticular, when the turbine is associated with an electric powergenerator, its speed of rotation can be exactly adjusted with the demandby the electric network in which the generator is inserted.

Moreover, a turbine according to the invention is marked by a simple andeconomic structure, which is adapted to make impulse turbines theworking members of each runner of which do not work in conditions of lowpressure, as instead happens in the reaction turbines, so that they donot run any risk of cavitation with the resulting erosion phenomena ofthe material which constitutes them.

A turbine according to the invention has also the remarkable advantageto allow a reversible operation, and to be therefore able to operateeither as a turbine in order to generate electric power by means of arespective generator, or as a pump in order to move a fluid mass whenthe generator associated with the turbine is fed so as to work like anelectric motor. The characteristic of the reversible operation of theturbine according to the invention makes it more adapted to be used toproduce energy in a hydroelectric power and pumping plant.

Further characteristics and advantages of the invention will become moreclearly evident from the following detailed description, made withreference the annexed drawings given purely by way of a non limitingexample, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a principle view showing the operation of a runner of animpulse turbine according to the prior art,

FIGS. 2, 3 and 4 are views similar to FIG. 1, which respectively showthe principle of operation of three different runners of a turbineaccording to the invention,

FIG. 5 is a schematic perspective view of a first embodiment of aturbine according to the invention,

FIG. 6 is a front elevational view of the turbine of FIG. 5, from arrowVI of such a figure,

FIG. 7 is a top elevational view of the turbine of FIGS. 5 and 6,partially sectioned at the shaft of the runner, from arrow VII of FIG.6,

FIG. 8 is a schematic perspective view of another embodiment of aturbine according to the invention,

FIG. 9 is a side elevational view of the turbine of FIG. 8 partiallysectioned at the shaft of the runner, from arrow IX of FIG. 8, and

FIG. 10 is a bottom elevational view of the turbine of FIGS. 8 and 9,from arrow X of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

With initial reference to FIGS. 2 to 4, a turbine runner 10 has at leasta hollow working member 12, having a generally arched shape, whichextends transversely to its axis of rotation, for example according to amore or less inclined configuration with respect to this axis and to theplane of FIGS. 2 to 4. Each working member 12 has an inlet portion 12 aat which a fluid having an absolute speed V is fed according to asubstantially transverse direction with respect to the axis of rotationof the runner 10. From a practical point of view, such a hollow workingmember can be made with a greater facility by means of a blade or atubular duct. Each working member 12 of the runner 10 has its inletportion directed tangentially with respect to the runner 10, towards thedirection from which the fluid comes, and a discharge portion 12 b fromwhich the fluid comes out after having lapped a bottom surface of themember 12.

Although in the continuation of the description a specific reference toan impulse turbine of hydraulic will be made, namely using water as aworking fluid, the invention can be applied also to an impulse turbineworking with other liquids, vapours or gas, with few changes at thereach of the skilled person. Moreover, a turbine according to theinvention, being of the reversible type, can also be used as a pump or acompressor.

In the operation of the machine as a turbine, the working fluid flowsalong the member 12 until it reaches the discharge portion 12 b, fromwhich it is discharged with a residual relative speed u which is smallerthan the inlet speed V (preferably almost zero), approximately parallelbut with a direction opposite to that of the speed V. The shape of theworking members 12, and in particular their curvature, can be selectedso as to obtain that the radius r, that is the distance of the straightline of action of the force F from the axis of rotation of the runner10, is such as to obtain a desired speed of rotation ω for a prefixedspeed V of the fluid.

As illustrated in particular in FIGS. 3 and 4, the inlet and dischargeportions 12 a and 12 b of each member 12 of the runner 10 are arrangedat opposite sides with respect to an imaginary plane of reference(schematized in these figures by a dotted line) which passes along theaxis of rotation of the runner 10 and is arranged perpendicularly to arectilinear segment joining the inlet and the discharge portions 12 aand 12 b of the member 12.

When the point at which the resultant F acts is located between theaforesaid plane of reference and the inlet portion 12 a of the member 12(FIG. 3), the speed of rotation ω of the runner 10 will have acounter-clockwise direction with respect to FIG. 3, so that the runner10 will tend to rotate in such way that the inlet portion 12 a of eachof its members 12 will move in agreement with the fluid fed to the inletportion of the same member 12.

When, instead, the point at which the resultant F acts is locatedbetween the plane of reference and the discharge portion 12 b of themember 12 (FIG. 4), the speed of rotation ω of the runner 10 will have aclockwise direction with respect to FIG. 4, so that the runner 10 willtend to rotate in such a way that each inlet portion 12 a of eachworking members 12 of it will move towards it. In this second event, thefluid will be fed to each member 12 with a speed corresponding to thesum of the absolute speed V of the fluid and the peripheral speed ofrotation of the input portion 12 a of the member 12 with respect to astationary zone of the machine, which will allow an increase of therelative flowing speed of the fluid along each member 12, which causes apositive effect on the speed of rotation of the runner 10.

In FIGS. 5 to 7 a first embodiment of a turbine according to theinvention is schematically illustrated, which has a runner 10 whoseworking members 12 are constituted by blades 12 having an open concavesection, which may have indifferently a geometry similar to thatillustrated in one of the FIGS. 2 to 4, as a function of theperformances that one desires to obtain from the machine.

The runner 10 is fast on a shaft 14 arranged horizontally, which definesthe axis of rotation of the runner 10. The shaft 14 is typicallysupported in rotation by at least a rolling bearing 16 and is connectedto the rotor of an electric current generator 18, such as an alternator.

The runner 10 is associated with a distributor unit 20 supported by abase 22 and crossed by the shaft 14. Inside the group 20, a verticalfeeding duct 24 coaxial with a fluid delivery pipe 26 is arranged, theduct 24 being tangentially coupled with a spiral-shaped circulationchamber 28 having, at a sidewall 30 of it, a circular outflow opening32, coaxial with the shaft 14. The opening 32 is encircled by acylindrical collar 34, preferably provided with a bent out edge 36 atits outside end, within which the inlet portions 12 a of the blades 12are arranged, while the discharge portions 12 b of each blade arearranged outside the collar 34. In order to make the assembly easier,the wall 30 is preferably divided into more portions, such as twosemi-portions 30 a and 30 b, each of which can be disassembled in anindependent way.

Conveniently, the distributor unit 20 comprises means for adjusting theflow rate of the fluid fed to the circulation chamber 28, which include,for example, a slab 38 slidably mounted along a direction indicated bydouble arrow A of FIG. 6, adapted to take a series of positions in whichit interferes with the flow of the fluid coming from the duct 24, indifferent ways. As an alternative to the slidable slab 38, a tabswingable about an axis of rotation parallel to the shaft 14, or athrottle arranged in the duct 24, may be provided. To the slab 38 or anyother device known per se for adjusting the flow rate, a device foropening outside the duct 24 (not illustrated) is convenientlyassociated, so as to allow, if necessary, the fluid coming from thedelivery pipe 26 to flow outside the distributor 20.

The movement of the slab 38 or any other member for adjusting the fluidflow rate admitted inside the unit 20, can be controlled by anyactuating device known per se (not illustrated) the driving of which canbe automatically controlled by means of sensors of the speed of rotationof the runner 10 and/or of the flow rate of the fluid passing throughthe delivery pipe 26.

Preferably, the discharge portion 12 b of each blade 12 of the runner 10is wider than the relative inlet portion 12 a, and the arched bottomsurface 13 thereof, which may be shaped as an arc of a circle,elliptical or spiral portion, extends by an angle a little smaller than180°, for example about 170°.

In order to allow the correct positioning of the inlet portions 12 a ofthe blades 12 inside the collar 34 of the distributor 20, and to avoidthat the portions 12 a of several blades 12 may cover each other, theblades 12 are arranged preferably with the centre line of their ownbottom surface 13 inclined with an angle a with respect to the axis ofrotation of the runner 10, which angle, at least for a runner 10provided with two facing blades 12, such as that illustrated in FIGS. 5to 7, may correspond to about 60°. Since a runner 10 of a turbineaccording to the invention can be provided with a single blade or withmore than two blades, as a function of the performances required to themachine and of its working conditions, the angle a may have severalvalue also substantially different from that indicated above, inparticular in the case of a number of blades different from two.

When the machine operates as a turbine, the fluid coming from the pipe26 passes along the tangential duct 24 until it reaches the circulationchamber 28 where it will be induced to rotate as a whirl according to acounter-clockwise direction, with reference to FIGS. 5 and 6. The fluidreaching the outflow opening 32 and the zone delimited by the collar 34,will be subjected to a whirling movement but it will also have an axialcomponent, usually small, in order to promote the uniform outflow of thefluid from the distributor 20. Therefore, the fluid reaching the opening32 will be fed to the inlet portions of the blades 12 according to adirection which is mainly tangential with respect to the axis ofrotation of the runner 10, so as to run along each blade 12 and togenerate a thrust action applied approximately at the centre of eachblade 12, in order to cause the runner 10 to rotate. After running alonga blade 12, the fluid is discharged outside the machine through therespective discharge portion 12 b.

As previously stated, an impulse turbine according to the invention canalso be used as a driven machine by applying a torque to the shaft 14 byan electric motor which may be the same generator 18 fed with anelectric current at its poles. In this working condition, the runner 10is driven into rotation and the portions 12 b of the ducts 12 will haveto be submerged by the working fluid, at least for a portion of theircircular motion about the axis of rotation of the runner 10, in such waythat such a fluid can be moved until the portions 12 a of each blade 12,and from these to the circulation chamber 28 and then to the pipe 26.

FIGS. 8 to 10, in which the same numeral references of FIGS. 5 to 7 havebeen used for indicating parts equal or similar to those of theembodiment previously described, illustrate schematically anotherembodiment of an impulse turbine according to the invention.

The runner 10 of this machine is bell-shaped and is provided with aseries of working members, for example six, each of which is constitutedby a tubular duct 12 formed in the thickness of the body of the runner10. Each duct 12 is helically wound with respect to the axis of rotationof the runner 10.

A shaft 14, which is supported vertically in rotation by at least arolling bearing 16, such as a thrust bearing, is fixed to the runner 10.

A delivery pipe 26 is arranged upstream the runner 10 to feed theworking fluid to the inlet portions 12 a of the tubular ducts 12. Thepipe 26 is substantially parallel to the shaft 24 at its zone close tothe runner 10, while in a zone more distant from the runner 10 it has abent or elbow portion 26 a. A through opening 27 is formed in theportion 26, to which seal means 27 a are associated through which theshaft 14 extends outside the pipe 26 in order to be connected with therotor of an electric current generator, typically an alternator (notillustrated). Conveniently, downstream the runner 10 a pipe with a largediameter is arranged for collecting the fluid, which is schematicallyindicated by a pair of parallel dotted lines.

Likewise to the previous embodiment, the machine according to thepresent embodiment is also conveniently provided with means foradjusting the flow rate of the fluid fed to the runner 10. These means,which are not illustrated in the figures, are arranged in the pipe 26upstream the elbow portion 26 a and include, for example, a throttleswingably mounted about an axis transverse to the axis of the pipe 26,or a spindle or “Larner-Johnson” type valve. Likewise to the previousembodiment, upstream such means for adjusting the flow rate is arrangeda device for opening outwards the pipe 26 (also not illustrated), whichis able to allow to discharge the fluid outside the pipe 26 in the caseof a stop of the plant.

Preferably, the body of the runner 10 is formed by two bell-shapedhalf-shells 10 a and 10 b coupled with each other by means of anyconnection means known per se. In particular, the first half-shell 10 ais fixed to the shaft 14 and has on its outside surface a series ofgrooves, for example having a square cross section, each of whichdefines the main part of the side surface of a respective tubular duct12. The second half-shell 10 b constitutes a kind of cover which can besuperimposed to the half-shell 10 a in order to close the side surfaceof the various tubular ducts 12.

Also in this case, the geometry of the tubular ducts 12 can be either ofthe type illustrated in FIG. 3 or of the type illustrated in FIG. 4.

The shaft 14, at its portion more adjacent to the inlet portions 12 a oftubular ducts 12, has a flaring or frustum of hyperboloid shaped portion11, whose curved flanks allow to better direct the flow of the fluidtowards the inlet portions 12 a.

Also in this case, the discharge portion 12 b of each tubular duct 12preferably has a section wider than the relative inlet portion 12 a, andeach tubular duct 12 extends by an angle which is a little smaller than180°, for example about 170°, as it is more clearly shown in FIG. 10.

When the machine operates as a turbine, the fluid fed through thedelivery pipe 26, which in this case performs the function of aninjector, reaches the fitting zone 11 of the shaft 14 at which it takesa substantially swirling movement in a plane perpendicular to the axisof the shaft 14, in order that it can be fed in a directionperpendicular to the mouth sections of the inlet portions 12 a of thetubular ducts 12, as indicated by arrow B of FIG. 10, and in an almosttangential direction with respect to the shaft 14. After the fluid haspassed through each duct 12, it is discharged from each duct 12 throughits discharge portion 12 b in the direction indicated by arrow C of FIG.10. As a result of the passage of the fluid inside of the various ducts12, the runner 10 is driven into rotation so as to drive the shaft 14and the equipments fast on it.

If a torque is applied to the shaft 14 to drive it into rotation, itsrotation will be transmitted to the runner 10 to allow the operation ofthe machine as a pump. In this case, the portion 12 b of the ducts 12should be submerged by the fluid in order to allow to draw it and takeit to the portion 12 a of each duct 12, and from here to the pipe 26.

It can be noticed that from the constructive point of view the machineof the present embodiment is simpler than the one of the previousembodiment, mainly because the spiral-shaped circulation chamber of thedistributor, with the relative outflow opening, is absent. Thisarrangement makes also the operation of the machine more practical whenit is used as a pump, since in this case the fluid drawn by the runner10 is sent directly to the pipe 26.

1. An impulse turbine, particularly of the reversible type, comprisingat least a runner fast on a shaft so as to be rotatable about an axis ofrotation, each runner being provided with at least a hollow workingmember adapted to receive a fluid fed according to a directionsubstantially transverse to said axis of rotation, from an inlet portionof the hollow working member to a discharge portion thereof, so that asa result of the passage of the fluid in the hollow working member thrustforces are generated whose resultant tends to drive said runner intorotation, wherein the distance between the straight line of action ofthe resultant of the thrust forces on each hollow working member and theaxis of rotation of the runner, is smaller than the distance between theinlet portion of each hollow working member and the axis of rotation ofthe runner.
 2. An impulse turbine according to claim 1, wherein theinlet portion of each working member of the runner opens towards adirection tangential to the runner.
 3. An impulse turbine according toclaim 2, wherein the discharge portion of each working member of therunner is wider than the relative inlet portion.
 4. An impulse turbineaccording to claim 3, wherein each working member of the runner isprovided with an arched bottom surface intended to allow said fluid toflow, for example having the shape of a portion of an arc of circle orof an ellipse, which extends by an angle a little smaller than 180°, asabout 170°.
 5. An impulse turbine according to claim 1, wherein eachworking member of the runner is such that the point at which theresultant of the thrust forces applied to it as a result of the slidingof the fluid acts, is located between the inlet portion of the workingmember and a plane of reference which passes along the axis of rotationof the runner and is perpendicular to a segment joining the inletportion and the discharge portion of the same working member, so thatthe runner tends to rotate in such a way that the inlet portion of eachworking member moves in agreement with the fluid fed to it.
 6. Animpulse turbine according to claim 1, wherein each working member of therunner is such that the point at which the resultant of the thrustforces applied to it as a result of the sliding of the fluid acts, islocated between the discharge portion of the working member and a planeof reference which passes along the axis of rotation of the runner andis perpendicular to a segment joining the inlet portion and thedischarge portion of same working member, so that the runner tends torotate in such a way that the inlet portion of each working member movestowards the fluid fed to it.
 7. An impulse turbine according to claim 1,wherein each working member of the runner is constituted by a blade withan open concave section, provided with an arched bottom surface.
 8. Animpulse turbine according to claim 7, wherein the runner comprises atleast a pair of opposed blades, the bottom surface of each blade havinga centre line which is located on a plane inclined of about 60° withrespect to the axis of rotation of the runner.
 9. An Impulse turbineaccording to claim 7, wherein each blade of the runner is fed with saidfluid by means of a distributor unit adapted to cause the delivery ofthe fluid in a direction mainly tangential with respect to a circularoutflow opening thereof, the runner being arranged coaxially with saidoutflow opening in such a way that the inlet portion of its blades arearranged within said outflow opening.
 10. An impulse turbine accordingto claim 9, wherein the distributor unit comprises a chamber for thecirculation of the fluid, which is delimited by a wall arrangedaccording to a generally spiral configuration, to which the fluid is fedthrough a tangential feeding duct.
 11. An impulse turbine according toclaim 10, wherein the distributor unit comprises means for adjusting theflow rate of the fluid fed to said circulation chamber, which include amember movable with respect to the circulation chamber and adapted totake a plurality of positions in which such a member interferes in adifferent measure with the flow of the fluid coming from the tangentialfeeding duct.
 12. An impulse turbine according to claim 1, wherein eachworking member of the runner is defined by a tubular duct formed withinthe thickness of a bell-shaped body, each tubular duct being wound in asubstantially helical manner with respect to the axis of rotation of therunner.
 13. An impulse turbine according to claim 12, wherein eachtubular duct of the runner is fed from a delivery pipe coaxial with theaxis of rotation of the runner.
 14. An impulse turbine according toclaim 13, wherein the runner is associated with a shaft arrangedcoaxially inside said delivery pipe, such a shaft extending outside thedelivery pipe at an elbow portion thereof.
 15. An impulse turbineaccording to claim 13, wherein the body of the runner includes first andsecond half-shells coupled to each other, a series of open channelsbeing formed in the first half-shell and the second half-shellconstituting a cover adapted to close said channels in its conditioncoupled with the first half-shell, so as to delimit a series of tubularducts.